Optical imaging and target detection through scattering media have been studied for use in aerospace, medical, military, and industrial applications. Conventional polarimetric-imaging techniques rely on the assumption that weakly scattered light maintains its initial polarization state, while highly scattered light does not. The, the polarization of scattered light actually depends upon a number of geometrical, and physical parameters.
The intensity of an image captured by interrogating a target with laser light can be altered by varying the polarization state of the incident laser light and changing the configuration of an analyzer to receive different polarization components of the backscattered light. Previous attempts to generate images based on the polarization state of backscattered light have focused on the loss of linear polarization through light-scattering media as detected by the analyzer. However, linear-polarized light tends to lose a significant degree of polarization in a large number of light-scattering media. Such attempts have failed to analyze the depolarization of circularly-polarized light, based on the Mueller-matrix concept, by detecting highly-scattered light from biologically-inspired phantoms as well as, to a lesser extent, from biological tissues.
Other approaches have been designed to enhance the appearance of images captured using optical imaging techniques. For example, enhancement of such images has been obtained by means of dual-energy imaging principles. The principles of dual-energy imaging involve the use of two optical images, one produced by interrogating the target with a high energy (low wavelength) light source, and another produced by interrogating the target with a low energy (high wavelength) light source. The target typically reflects the high-energy light differently than it does the low-energy light. A weighted subtraction of these two images can produce a sharply-contrasted digital image which minimizes the appearance of interfering background structures.
An additional technique known for enhancing imaging applications is the use of focal-length scanning devices. Focal length scanning of the target is performed by varying the focal depth of a lens positioned to direct the light used for interrogating the target. This essentially illuminates a single “slice” of the target located a predetermined distance from the lens in the axial direction of the propagating light. The process is continuously repeated for several different focal depths until the entire three-dimensional target has been captured as an image. But again, this hardware-based super-resolution approach does not provide a desirable contrast between the target and interfering background noise.
Several studies have been conducted to evaluate the exploitation of a dual-rotating retarder complete-Mueller polarimeter. However, none of these studies have fused dual-energy capabilities with polarimetric measurements. Furthermore, there exist other studies involving the exploitation of dual-rotating polarizer incomplete polarimeter configuration for aerospace, and medical imaging applications. But since the polarimeters involved in these studies are incomplete, they do not take into account elliptical polarization states. And again, these studies do not contemplate the fusion of dual-energy techniques with polarimetric imaging principles. Finally, the exploitation of polarization principles fused with dual-energy capabilities has been proposed, but such proposals have all neglected to incorporate the means of dual-rotating retarder complete polarimeter.
Accordingly, there is a need in the art for an imaging system that can yield improved images with reduced noise, high specificity, and high contrast. The system should be a complete polarimeter and analyze the depolarization of circularly-polarized light, based on the Mueller-matrix concept, by detecting highly-scattered light from biologically-inspired phantoms as well as from biological tissues. Such a system should provide enhanced imaging capabilities for homeland security, biomedical, industrial, aerospace applications. Further, the optical fusion sensor system should possess imaging capabilities over a wide spectral bandwidth, while providing a desirable battleship awareness by rapid detection, location and recognition of enemy targets in highly cluttered environments. In addition, the system should be combinable with an active or passive multispectral spectropolarimeter or multispectral imaging system for enhanced imaging, and should prove useful should exhibit improved performance in adverse atmospheric and ambient environmental conditions.